The use of pre-shaped rigid bodies of calcium silicate hydrates as high temperature thermal insulation has long been known, and several processes for the manufacture thereof are also known. Such prior practice has included heating aqueous slurries of reactive calcareous and siliceous materials under either atmospheric or super-atmospheric pressure to at least partially react said calcareous and siliceous materials. Where this initial (pre-shaping) reaction has been conducted at atmospheric pressure it has normally been found necessary to complete the hydrothermal reaction by treating the shaped ware with saturated steam at superatmospheric pressure in order to produce satisfactory products. In such processes the partially reacted and fluent slurry can be placed into so-called pan molds of desired shape and then cured in an autoclave while still in the pan molds and without preliminary dewatering. Alternatively, the partially reacted slurry can be shaped in so-called filter press molds of the desired configuration, with expression of sufficient aqueous medium therefrom to permit removal of the shaped ware from the mold for subsequent autoclaving to complete the hydrothermal cure reaction. However, where the initial (pre-shaping) hydrothermal reaction is carried out to sufficient completion in the presence of saturated steam at superatmospheric pressures, it has been suggested that it may be possible to omit such post-shaping treatment and to obtain satisfactory products by merely drying the shaped ware. Small amounts of fibrous reinforcement have frequently been included in these prior art hydrous calcium silicate products.
The use as high temperature thermal insulation of pre-shaped rigid bodies composed of expanded inorganic aggregate, such as expanded perlite or vermiculite, bonded with inorganic compositions such as alkali metal silicates, is also known. Such products can be manufactured by mixing the expanded aggregate with an aqueous solution of alkali metal silicate, compacting this mixture into the desired shape, curing (as by including a suitable curing agent and/or by heating) to insolubilize the binder and finally drying.
The use of a quasi-colloidal gel containing mixed crystals of calcium silicate hydrate, calcium alumino-silicate hydrate and calcium aluminate hydrate, made by reacting calcium oxide or hydroxide with perlite dust in a molar ratio of SiO.sub.2 :CaO of about 1.1 to 2.0 in the presence of sufficient water to produce a dough-like material and subsequently adding more water and heating at 60.degree.-95.degree. C., as a bonding agent for expanded perlite and/or vermiculite has been disclosed in U.S. Pat. No. 3,590,111. The shaped ware requires autoclaving in saturated steam at superatmospheric pressures before drying to form the final rigid product. The pre-shaping reactions to form the binding agent gel are disclosed to be conducted at atmospheric pressure.
While certain of these prior art products, and the corresponding methods of producing them, have achieved a degree of commercial success, they have all been found to suffer from various deficiencies which the present invention largely overcomes. For example, calcium silicate hydrate products molded from slurries of calcareous and siliceous reactants which have not been reacted at superatmospheric pressures before molding require expensive and time-consuming post-curing in the presence of saturated steam at superatmospheric pressures. While such post-molding autoclaving may not always be required where a slurry of calcareous and siliceous reactants is sufficiently pre-reacted in the presence of saturated steam at superatmospheric pressure, it has been found difficult to consistently produce acceptable products by such processes and such pre-reacted calcium silicate hydrate gels release water very slowly so that press molding cycles are undesirably protracted. These problems are especially pronounced with products of low density. The prior art expanded inorganic aggregate products bonded with alkali silicate binders are found to suffer excessive erosion by abrasion in handling, installation and use, and to have lower compressive strength and impact resistance as compared to prior art calcium silicate hydrate products not containing expanded aggregate.